Alternate Sires in Pedigrees
In studying pedigrees, one sometimes runs across a horse shown as being by one of two or sometimes even three sires--for instance, 1951 King George VI and Queen Elizabeth Stakes winner Supreme Court, whose entry in the General Stud Book shows him as being by Persian Gulf or Precipitation. These entries are the result of a mare's having been covered by more than one sire during the breeding season, leaving uncertainty as to which stallion is the actual father of the foal in question.
Convention versus reality
Traditionally, in cases in which a mare was mated to more than one sire during the breeding season, the sires are listed in the order in which they covered the mare, and the last stallion in the sequence is normally presumed to be the actual father of the foal. Since the usual reason for the second mating would be that the mare came back into heat after the first one, the assumption is that she came back into heat because she was not pregnant.
Unfortunately, this isn't always the case. Sometimes a mare will show heat and accept a stallion's services even if she is in early pregnancy. Comparing foaling dates to dates of service cannot always be relied on either as the length of an equine pregnancy is fairly variable. In his book Bloodstock Breeding, Sir Charles Leicester cites the case of the mare Agnostic, who was covered on May 25 and May 29 of 1934 by the stallion Vanoc. By June of 1935, she had not produced a foal and came back into heat. She was covered by the stallion Friendship on June 19 but on July 3 produced a colt, presumably from one of her matings with Vanoc since there was no record of her having been covered by any other stallion. Because of cases like this, the most that could be said prior to modern DNA typing was that a foal was probably by the last stallion to have covered the mare unless the foal evidenced a dominant trait that one sire had and the other did not (such as gray coloring).
Adding to the confusion, recorders in days gone by did not always adhere to the convention of listing the sires in the order in which they covered the mare or might leave out the name of one covering sire because of a conviction that the foal was in fact fathered by the other. Thus, multiple coverings have helped generate pedigrees for the same horse which are contradictory as to paternity.
In the modern era
Thanks to DNA typing, there is now no question about the parentage of a foal even if a mare was covered by two or more sires in the same breeding season. Unfortunately, the current state of genetic testing is unable to sort out the true paternity of most of the horses conceived after multiple matings in days gone by, leaving some pedigrees dating back no more than 40 or 50 years with some degree of ambiguity.
Convention versus reality
Traditionally, in cases in which a mare was mated to more than one sire during the breeding season, the sires are listed in the order in which they covered the mare, and the last stallion in the sequence is normally presumed to be the actual father of the foal. Since the usual reason for the second mating would be that the mare came back into heat after the first one, the assumption is that she came back into heat because she was not pregnant.
Unfortunately, this isn't always the case. Sometimes a mare will show heat and accept a stallion's services even if she is in early pregnancy. Comparing foaling dates to dates of service cannot always be relied on either as the length of an equine pregnancy is fairly variable. In his book Bloodstock Breeding, Sir Charles Leicester cites the case of the mare Agnostic, who was covered on May 25 and May 29 of 1934 by the stallion Vanoc. By June of 1935, she had not produced a foal and came back into heat. She was covered by the stallion Friendship on June 19 but on July 3 produced a colt, presumably from one of her matings with Vanoc since there was no record of her having been covered by any other stallion. Because of cases like this, the most that could be said prior to modern DNA typing was that a foal was probably by the last stallion to have covered the mare unless the foal evidenced a dominant trait that one sire had and the other did not (such as gray coloring).
Adding to the confusion, recorders in days gone by did not always adhere to the convention of listing the sires in the order in which they covered the mare or might leave out the name of one covering sire because of a conviction that the foal was in fact fathered by the other. Thus, multiple coverings have helped generate pedigrees for the same horse which are contradictory as to paternity.
In the modern era
Thanks to DNA typing, there is now no question about the parentage of a foal even if a mare was covered by two or more sires in the same breeding season. Unfortunately, the current state of genetic testing is unable to sort out the true paternity of most of the horses conceived after multiple matings in days gone by, leaving some pedigrees dating back no more than 40 or 50 years with some degree of ambiguity.